▲ 1265 ▼ Panik (i.postimg.cc) submitted 2 years ago by ickplant@lemmy.world to c/lemmyshitpost@lemmy.world 146 comments fedilink hide all child comments
[–] Dagwood222@lemm.ee 30 points 2 years ago (3 children) Any number where the individual digits add up to a number divisible by '3' is divisible by 3. 51 = 5+1 = 6, which is divisible by three. Try it, you'll see it always works. permalink fedilink source hideshow 6 child comments replies: [–] letsgo@lemm.ee 8 points 2 years ago (3 children) There are tricks like that for a lot of numbers. For 7, chop off the last digit, double it and add it to what's left. Repeat as required. If the result is divisible by 7 then the original number was. eg: 356 -> 35+12=47 not db7. 357 =>35+14 both db7 so we don't even need to do the add. permalink fedilink source parent hideshow 6 child comments replies: [–] Dagwood222@lemm.ee 5 points 2 years ago (1 child) Clever. permalink fedilink source parent hideshow 2 child comments replies: [–] Klear@sh.itjust.works 3 points 2 years ago Girl. permalink fedilink source parent [–] diverging@lemmy.ml 3 points 2 years ago double it and add it to subtract it from what’s left permalink fedilink source parent [–] BruceDoh@sh.itjust.works 1 point 2 years ago (1 child) 14: 1 + 8 = 7. Not db7 permalink fedilink source parent hideshow 2 child comments replies: [–] sockenklaus@sh.itjust.works 3 points 2 years ago (1 child) You clearly mean: 14: 1 + 8 = 9 (not db 7) Someone else in this thread correctly stated: "Chop of last digit, double it and subtract from what is left" 14: 1 - 8 = -7. (dB 7!) Math is awesome, I didn't know this trick! permalink fedilink source parent hideshow 2 child comments replies: [–] BruceDoh@sh.itjust.works 1 point 2 years ago Yes, that's what I meant. The subtract rule works. permalink fedilink source parent [–] Zacryon@feddit.de 5 points 2 years ago (1 child) One of the reasons why I love the number 3. There are other neat digit sum tricks, see for example for the numbers 1 to 30 here: https://en.m.wikipedia.org/wiki/Divisibility_rule permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 7 points 2 years ago (2 children) They didn't teach stuff like this in school, which is silly. This is the kind of thing that a kid would eat up. It's like they wanted to make sure people hated math. permalink fedilink source parent hideshow 4 child comments replies: [–] steeznson@lemmy.world 4 points 2 years ago My experience of maths in high school was being taught a trick or method to solve a really specific type of problem every week. Sometimes the method would build off something we'd learnt the previous week. The whole thing was bottom-up learning where you get given piecemeal nuggets of information but never see the big picture. They completely lost me at around the age of 15. I eventually came back to maths later in life after studying formal logic in my philosophy undergrad degree. permalink fedilink source parent [–] Zacryon@feddit.de 2 points 2 years ago (1 child) I guess I was one of the lucky few who learned this in elementary school. And later again. permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 1 point 2 years ago (1 child) I first saw the nine times finger trick in the movie 'Stand And Deliver.' I remember seeing it written out on a blackboard at some point, but never the finger trick. https://youtu.be/-WOgLltWhgg permalink fedilink source parent hideshow 2 child comments replies: [–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent [–] Laukidh@infosec.pub 3 points 2 years ago* (1 child) I knew that worked with 9. Hmm, does it work with 6? Doesn’t look like it. permalink fedilink source parent hideshow 2 child comments replies: [–] AEsheron@lemmy.world 1 point 2 years ago* Technically it does work for 6, more literally, still aiming for 3, not 6. That's half of it, if the starting number is even and divisible by 3 then it is also divisible by 6. permalink fedilink source parent
[–] letsgo@lemm.ee 8 points 2 years ago (3 children) There are tricks like that for a lot of numbers. For 7, chop off the last digit, double it and add it to what's left. Repeat as required. If the result is divisible by 7 then the original number was. eg: 356 -> 35+12=47 not db7. 357 =>35+14 both db7 so we don't even need to do the add. permalink fedilink source parent hideshow 6 child comments replies: [–] Dagwood222@lemm.ee 5 points 2 years ago (1 child) Clever. permalink fedilink source parent hideshow 2 child comments replies: [–] Klear@sh.itjust.works 3 points 2 years ago Girl. permalink fedilink source parent [–] diverging@lemmy.ml 3 points 2 years ago double it and add it to subtract it from what’s left permalink fedilink source parent [–] BruceDoh@sh.itjust.works 1 point 2 years ago (1 child) 14: 1 + 8 = 7. Not db7 permalink fedilink source parent hideshow 2 child comments replies: [–] sockenklaus@sh.itjust.works 3 points 2 years ago (1 child) You clearly mean: 14: 1 + 8 = 9 (not db 7) Someone else in this thread correctly stated: "Chop of last digit, double it and subtract from what is left" 14: 1 - 8 = -7. (dB 7!) Math is awesome, I didn't know this trick! permalink fedilink source parent hideshow 2 child comments replies: [–] BruceDoh@sh.itjust.works 1 point 2 years ago Yes, that's what I meant. The subtract rule works. permalink fedilink source parent
[–] Dagwood222@lemm.ee 5 points 2 years ago (1 child) Clever. permalink fedilink source parent hideshow 2 child comments replies: [–] Klear@sh.itjust.works 3 points 2 years ago Girl. permalink fedilink source parent
[–] diverging@lemmy.ml 3 points 2 years ago double it and add it to subtract it from what’s left permalink fedilink source parent
[–] BruceDoh@sh.itjust.works 1 point 2 years ago (1 child) 14: 1 + 8 = 7. Not db7 permalink fedilink source parent hideshow 2 child comments replies: [–] sockenklaus@sh.itjust.works 3 points 2 years ago (1 child) You clearly mean: 14: 1 + 8 = 9 (not db 7) Someone else in this thread correctly stated: "Chop of last digit, double it and subtract from what is left" 14: 1 - 8 = -7. (dB 7!) Math is awesome, I didn't know this trick! permalink fedilink source parent hideshow 2 child comments replies: [–] BruceDoh@sh.itjust.works 1 point 2 years ago Yes, that's what I meant. The subtract rule works. permalink fedilink source parent
[–] sockenklaus@sh.itjust.works 3 points 2 years ago (1 child) You clearly mean: 14: 1 + 8 = 9 (not db 7) Someone else in this thread correctly stated: "Chop of last digit, double it and subtract from what is left" 14: 1 - 8 = -7. (dB 7!) Math is awesome, I didn't know this trick! permalink fedilink source parent hideshow 2 child comments replies: [–] BruceDoh@sh.itjust.works 1 point 2 years ago Yes, that's what I meant. The subtract rule works. permalink fedilink source parent
[–] BruceDoh@sh.itjust.works 1 point 2 years ago Yes, that's what I meant. The subtract rule works. permalink fedilink source parent
[–] Zacryon@feddit.de 5 points 2 years ago (1 child) One of the reasons why I love the number 3. There are other neat digit sum tricks, see for example for the numbers 1 to 30 here: https://en.m.wikipedia.org/wiki/Divisibility_rule permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 7 points 2 years ago (2 children) They didn't teach stuff like this in school, which is silly. This is the kind of thing that a kid would eat up. It's like they wanted to make sure people hated math. permalink fedilink source parent hideshow 4 child comments replies: [–] steeznson@lemmy.world 4 points 2 years ago My experience of maths in high school was being taught a trick or method to solve a really specific type of problem every week. Sometimes the method would build off something we'd learnt the previous week. The whole thing was bottom-up learning where you get given piecemeal nuggets of information but never see the big picture. They completely lost me at around the age of 15. I eventually came back to maths later in life after studying formal logic in my philosophy undergrad degree. permalink fedilink source parent [–] Zacryon@feddit.de 2 points 2 years ago (1 child) I guess I was one of the lucky few who learned this in elementary school. And later again. permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 1 point 2 years ago (1 child) I first saw the nine times finger trick in the movie 'Stand And Deliver.' I remember seeing it written out on a blackboard at some point, but never the finger trick. https://youtu.be/-WOgLltWhgg permalink fedilink source parent hideshow 2 child comments replies: [–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent
[–] Dagwood222@lemm.ee 7 points 2 years ago (2 children) They didn't teach stuff like this in school, which is silly. This is the kind of thing that a kid would eat up. It's like they wanted to make sure people hated math. permalink fedilink source parent hideshow 4 child comments replies: [–] steeznson@lemmy.world 4 points 2 years ago My experience of maths in high school was being taught a trick or method to solve a really specific type of problem every week. Sometimes the method would build off something we'd learnt the previous week. The whole thing was bottom-up learning where you get given piecemeal nuggets of information but never see the big picture. They completely lost me at around the age of 15. I eventually came back to maths later in life after studying formal logic in my philosophy undergrad degree. permalink fedilink source parent [–] Zacryon@feddit.de 2 points 2 years ago (1 child) I guess I was one of the lucky few who learned this in elementary school. And later again. permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 1 point 2 years ago (1 child) I first saw the nine times finger trick in the movie 'Stand And Deliver.' I remember seeing it written out on a blackboard at some point, but never the finger trick. https://youtu.be/-WOgLltWhgg permalink fedilink source parent hideshow 2 child comments replies: [–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent
[–] steeznson@lemmy.world 4 points 2 years ago My experience of maths in high school was being taught a trick or method to solve a really specific type of problem every week. Sometimes the method would build off something we'd learnt the previous week. The whole thing was bottom-up learning where you get given piecemeal nuggets of information but never see the big picture. They completely lost me at around the age of 15. I eventually came back to maths later in life after studying formal logic in my philosophy undergrad degree. permalink fedilink source parent
[–] Zacryon@feddit.de 2 points 2 years ago (1 child) I guess I was one of the lucky few who learned this in elementary school. And later again. permalink fedilink source parent hideshow 2 child comments replies: [–] Dagwood222@lemm.ee 1 point 2 years ago (1 child) I first saw the nine times finger trick in the movie 'Stand And Deliver.' I remember seeing it written out on a blackboard at some point, but never the finger trick. https://youtu.be/-WOgLltWhgg permalink fedilink source parent hideshow 2 child comments replies: [–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent
[–] Dagwood222@lemm.ee 1 point 2 years ago (1 child) I first saw the nine times finger trick in the movie 'Stand And Deliver.' I remember seeing it written out on a blackboard at some point, but never the finger trick. https://youtu.be/-WOgLltWhgg permalink fedilink source parent hideshow 2 child comments replies: [–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent
[–] PipedLinkBot@feddit.rocks [B] 1 point 2 years ago Here is an alternative Piped link(s): https://piped.video/-WOgLltWhgg Piped is a privacy-respecting open-source alternative frontend to YouTube. I'm open-source; check me out at GitHub. permalink fedilink source parent
[–] Laukidh@infosec.pub 3 points 2 years ago* (1 child) I knew that worked with 9. Hmm, does it work with 6? Doesn’t look like it. permalink fedilink source parent hideshow 2 child comments replies: [–] AEsheron@lemmy.world 1 point 2 years ago* Technically it does work for 6, more literally, still aiming for 3, not 6. That's half of it, if the starting number is even and divisible by 3 then it is also divisible by 6. permalink fedilink source parent
[–] AEsheron@lemmy.world 1 point 2 years ago* Technically it does work for 6, more literally, still aiming for 3, not 6. That's half of it, if the starting number is even and divisible by 3 then it is also divisible by 6. permalink fedilink source parent
